Does the universe behave the same everywhere? Weak gravitational lenses may provide the answer

Research published in the Journal of Cosmology and Astroparticle Physics (JCAP) demonstrates how to test the assumptions of uniformity and isotropicity of the universe, known as cosmological principles. Images collected by new observatory such as the Euclidean Space Telescope. Finding evidence of anomalies in cosmological principles can have deep meaning in our current understanding of the universe.

“Cosmological principles are like a statement of ultimate humility,” explains James Adam, an astrophysicist at the University of the Western Cape, Cape Town, South Africa, and lead author of the new paper. According to cosmology principles, we are not only at the heart of the universe, but there is no true center.

A further assumption is that, distinct from uniformity, but independent, means that the universe is also isotropic, with no favorable orientation. These assumptions underlie the standard model of cosmology, the theoretical framework used to explain the origin, evolution and current state of the universe. Currently, it is the most robust and consistent model tested by many scientific observations, but it is not yet perfect.

In fact, some recent cosmological observations suggest that on very large scales there may be anisotropy in the structure of the universe that challenges isotropic assumptions.

These anomalies have been identified using different methods, including conflicting measurements of the expansion rate of the universe, studies of the background radiation of cosmic microwaves, and various inconsistencies in space data. However, these observations are not yet conclusive.

To rule out measurement errors, more data must be collected using independent methodologies. If multiple techniques confirm the same anomalies, their presence becomes much more difficult to reject.

A new study published in JCAP by Adam and colleagues has developed a new methodology for testing the isotropy of the universe using observations from instruments like Euclidean. Euclid is an ESA space telescope released in 2023 and has just begun creating images of the universe with unprecedented forces, accuracy and resolution.

“We investigated alternative ways to constrain anisotropy, including so-called weak gravity lenses,” Adam says. A weak lens occurs as matter between us and the distant galaxy slightly bends the galaxy’s light and changes its apparent shape. This particular type of distortion can reveal whether anisotropy exists in the universe.

In fact, analysis of weak lens data allows scientists to separate signals into two components: e-mode shear produced by isotropic and uniform distribution of matter in the universe, and usually very Do not display on a large scale in the weak B-mode shear isotropic universe.

These signals are very weak and can be attributed to measurement errors and quadratic effects, so simply observing the B mode on a large scale is not sufficient.

If anisotropy is realistic, it affects both e-mode and B-mode in a non-independent manner, generating a correlation between the two signals. Only when Euclid data reveals a significant correlation between E-mode and B modes would suggest an expansion of the anisotropy of the universe.

Meaning that can be considered as the next step

In their study, Adam and colleagues developed a model that simulates the effect of anisotropic universe expansion on computers and explains how isotropic deviations can correct weak lending signals.

We then calculate the EB cross-correlation to demonstrate that the anisotropic universe generates a correlation between two signals, and apply the model to future Euclidean data, and these observations can be used to potential anisotropy. was shown to be accurate enough to detect.

Euclid is already beginning to provide useful data for these analyses, and the new observatory will soon be online. As they developed the right methodology, Adam and his colleagues intend to apply it to actual data.

“When it’s kind of a quarter, especially in the later universe, we need to seriously consider whether this basic assumption is actually true.

If these anomalies are identified, we will open a new chapter in cosmology. However, that’s not easy. Although there are already alternative theoretical models that predict anisotropy, none are as robust or widely accepted as standard models.

However, the theoretical modifications also depend on the degree of anisotropy that may be detected, which remains uncertain. “It could be a serious revision,” concludes Adam.